In conventional microstrip antenna array configurations, mutual coupling between antenna elements is often considered undesirable because such coupling typically reduces antenna gain and diverts antenna power into unwanted sidelobes. However, in several known microstrip antenna configurations, mutual coupling has been used for specific effects between the driven antenna element and parasitic patches.
The article entitled "Microstrip Antenna Array with Parasitic Elements", by K. F. Lee et al., published in IEEE AP-S SYMPOSIUM DIGEST, Jun., 1987, pp 794-797, shows the use of parasitic patches placed around a single driven element to increase the gain by several decibels.
The article by S. A. Long and M. D. Walton entitled "A Dual-Frequency Stacked Circular Disc Antenna", published in IEEE Trans. Antenna and Propagation, Col. AP-27, Mar. 1979 shows the use of stacked parasitic patches developed to enhance the bandwidth of a microstrip radiator.
Parasitic patches with open circuit stubs have been used to shape the beam of an antenna so that its peak can be tilted in a desired direction as shown in the article by M. Haneishi et al., entitled "Beam-Shaping of Microstrip Antenna by Parasitic Elements having Coaxial Stub" published in Trans. IECE of Japan, vol. 69-B, pp 1160-1161, 1986.
In order to modify beam patterns, conventional microstrip array antennas often utilize power dividers and/or phase delay transmission lines, or the equivalent, which reduce array efficiency and increase array size.
Highly directional dipole antenna configurations are well known, such as the YAGI dipole antenna described originally in the article entitled "Beam Transmission of Ultra Short Waves" by H. Yagi in Proc. IRE, vol. 16, pp 715-741, Jun. 1928. Yagi antennas produce substantial directivity by use of parasitic director and reflector dipoles coplanar with the driven dipole. Ground planes, when used with Yagi antennas, must typically be positioned at least one quarter wavelength away from the plane of the elements to prevent unwanted cancellation between the radiated signal and the reflected signals from the groundplane.
The physical configuration of conventional Yagi dipole arrays are discussed, for example, in the article by C. A. Chen and D. K. Cheng entitled "Optimum Element Lengths for Yagi-Uda Arrays" published in IEEE Trans. Antennas and Propagation, vol. AP-23, Jan. 1975.
The current trends in antenna designs, such as those required by mobile, satellite linked communications systems, result in a need for low profile, directional microstrip antenna configurations which can conveniently be made to conform to the shape of the mobile unit, such as an airplane wing, while providing the highly directional antenna patterns achievable with other antenna configurations, such as those achievable with Yagi dipole antenna arrays.